1. Field of the Invention
The present invention relates to gas discharge display and memory devices. More particularly, the present invention relates to AC gas discharge display and memory devices having a nondestructive cursor function for displaying cursors for a variety of applications, such as computer graphics.
2. Description of the Prior Art
Gas discharge display and memory panels of the type to which the present invention pertains are well known in the art. For example, U.S. Pat. No. 3,499,167 to Baker et al describes such a panel. The gas panels of the type to which the present invention is directed typically have two glass plates maintained in spaced-apart relationship, and are arranged to have sealed between the spaced-apart plates an ionizable medium. To provide matrix addressability whereby selected local regions within the ionizable medium may be selectively ionized, sets of horizontal and vertical conductors are employed. Typically, the set of horizontal conductors comprises an array of parallel insulated conductors arranged on the inner surface of one plate and horizontally extending thereacross. Likewise, the set of vertical conductors comprise an array of parallel insulated conductors arranged on the inner surface of the other plate vertically extending thereacross, generally orthogonal to the horizontal conductors.
In such an arrangement, when an appropriate voltage is applied between a selected one of the horizontal conductors and a selected one of the vertical conductors, ionization occurs at the crossover point of the two conductors, such that light is emitted. Generally, the crossover points are referred to as "cells" and a display pattern or image is formed by ionizing selected cells. As another example of a panel as described and to which the present invention pertains, reference is made to an article by D. L. Bitzer et al entitled, "The Plasma Display Panel -- A Digitally Addressable Display with Inherent Memory," Proceedings of the Fall Joint Computer Conference IEEE, San Francisco, Calif., November 1966, pp. 541-547.
Although the cursor function has been implemented in prior art AC gas discharge display and memory panels, such prior art implementations are such as to cause the information previously stored in those cells used to form the cursor, to be erased. Accordingly, the information stored within these cells would necessarily have to be regenerated by writing from an external memory after the cursor is moved or else the information is permanently lost. Thus, not only did such prior art cursor functions necessitate the use of an external memory for purposes of regenerating the former information state lost as a result of the formation of a cursor, but in addition, such cursor functions necessarily involved additional control circuitry to control the regeneration. As an example of such prior art cursor functions, reference is made to that described by Tucker et al in U.S. Pat. No. 3,852,721.